Large tunneling frequencies of the symmetric tops NH3D+ and NHD+3 in crystalline fields of low symmetry

The tunneling frequencies of the symmetric tops NH3D+ and NHD+3 in ammonium compounds have been found to be large when the site symmetry for the ammonium ion is less than tetrahedral. The rotational potential function of these symmetric tops are derived from atom–atom potentials of the Buckingham (exp‐6) type. The tunneling frequencies of these symmetric tops, as well as their librational frequencies, have been computed in NH4F, NH4HF2, (NH4)2SiF6, (NH4)2GeF6, (NH4)2TiF6, NH4ReO4, NH4IO4, and NH4ClO4. In all these compounds, the computed tunneling frequencies are much larger than would have ordinarily been expected.